Think back to last Halloween for a minute. Wherever you looked,
there were vampires, ghosts, or bony skeletons grinning back at
you. Vampires and ghosts don't really exist, but skeletons sure
do! Every single person has a skeleton made up of many bones. These
bones give your body structure, let you move in many ways, protect
your internal organs, and more. It's time to look at all your
bones - the adult human body has 206 of them!
What Are Bones Made Of?
If you've ever seen a real skeleton or fossil in a museum,
you might think that all bones are dead. Although bones in museums
are dry, hard, or crumbly, the bones in your body are different.
The bones that make up your skeleton are all very much alive,
growing and changing all the time like other parts of your
body.
Almost every bone in your body is made of the same
materials:
- The outer surface of bone is called the
periosteum
(say: pare-ee-
os
-tee-um). It's a thin, dense membrane that contains nerves
and blood vessels that nourish the bone.
- The next layer is made up of
compact
bone. This part is smooth and very hard. It's the part you
see when you look at a skeleton.
- Within the compact bone are many layers of
cancellous
(say:
kan
-seh-lus) bone, which looks a bit like a sponge. Cancellous bone
is not quite as hard as compact bone, but it is still very
strong.
- In many bones, the cancellous bone protects the innermost
part of the bone, the
bone marrow
(say:
mar
-oh). Bone marrow is sort of like a thick jelly, and its job is
to make blood cells.
How Bones Grow
When you were a baby, you had tiny hands, tiny feet, and tiny
everything! Slowly, as you grew older, everything became a bit
bigger, including your bones.
A baby's body has about 300 bones at birth. These eventually
fuse (grow together) to form the 206 bones that adults have. Some
of a baby's bones are made entirely of a special material
called
cartilage
(say:
car
-til-ij). Other bones in a baby are partly made of cartilage. This
cartilage is soft and flexible. During childhood, as you are
growing, the cartilage grows and is slowly replaced by bone, with
help from
calcium
.
By the time you are about 25, this process will be
complete. After this happens, there can be no more growth -
the bones are as big as they will ever be. All of these bones make
up a skeleton that is both very strong and very light.
Your Spine
Your spine is one part of the skeleton that's easy to check
out: Reach around to the center of your back and you'll feel
its bumps under your fingers.
The spine lets you twist and bend, and it holds your body
upright. It also protects the spinal cord, a large bundle of nerves
that sends information from your brain to the rest of your body.
The spine is special because it isn't made of one or even two
bones: It's made of 26 bones in all! These bones are called
vertebrae
(say:
vur
-tuh-bray), and each one is shaped like a ring.
There are different types of vertebrae in the spine, and each
does a different kind of job:
- The first seven vertebrae at the top are called the
cervical
(say:
sir
-vih-kul) vertebrae. These bones are in the back of your neck,
just below your brain, and they support your head and neck. Your
head is pretty heavy, so it's lucky to have help from the
cervical vertebrae!
- Below the cervical vertebrae are the
thoracic
(say: thuh-
rah
-sick) vertebrae, and there are 12 in all. These guys anchor your
ribs in place.
- Below the thoracic vertebrae are five
lumbar
(say:
lum
-bar) vertebrae.
Beneath the lumbar vertebrae is the
sacrum
(say:
say
-krum), which is made up of five vertebrae that are fused together
to form one single bone. Finally, all the way at the bottom of the
spine is the
coccyx
(say:
cok
-sicks), which is one bone made of four fused vertebrae. The bottom
sections of the spine are important when it comes to bearing weight
and giving you a good center of gravity. So when you pick up a
heavy
backpack
, the lumbar vertebrae, sacrum, and coccyx give you the power. When
you dance, skip, and even walk, these parts help keep you
balanced.
In between each vertebra (the name for just one of the
vertebrae) are small
disks
made of cartilage. These disks keep the vertebrae from rubbing
against one another, and they also act as your spine's natural
shock absorbers. When you jump in the air, or twist while slamming
a dunk, the disks give your vertebrae the cushioning they need.
Your Ribs
Your
heart
,
lungs
, and liver are all very important, and luckily you've got ribs
to keep them safe. Ribs act like a cage of bones around your chest.
It's easy to feel the bottom of this cage by running your
fingers along the sides and front of your body, a few inches below
your heart. If you breathe in deeply, you can easily feel your ribs
right in the front of your body, too. Some thin kids can even see a
few of their ribs right through their skin.
Your ribs come in pairs, and the left and right sides of each
pair are exactly the same. Most people have 12 pairs of ribs, but
some people are born with one or more extra ribs, and some people
might have one pair less.
All 12 pairs of ribs attach in the back to the spine, where they
are held in place by the thoracic vertebrae. The first seven pairs
of ribs attach in the front to the
sternum
(say:
stur
-num), a strong bone in the center of your chest that holds those
ribs in place. The remaining sets of ribs don't attach to the
sternum directly. The next three pairs are held on with cartilage
to the ribs above them.
The very last two sets of ribs are called
floating
ribs because they aren't connected to the sternum or the ribs
above them. But don't worry, these ribs can't ever float
away. Like the rest of the ribs, they are securely attached to the
spine in the back.
Your Skull
Your skull protects the most important part of all, the brain.
You can feel your skull by pushing on your head, especially in the
back a few inches above your neck. The skull is actually made up of
different bones. Some of these bones protect your
brain
, whereas others make up the structure of your face. If you touch
beneath your eyes, you can feel the ridge of the bone that forms
the hole where your
eye
sits.
And although you can't see it, the smallest bone in your
whole body is in your head, too. The stirrup bone behind your
eardrum is only .1 to .13 inches (2.5 to 3.3 millimeters) long!
Want to know something else? Your lower jawbone is the only bone in
your head you can move. It opens and closes to let you talk and
chew food.
Your skull is pretty cool, but it's changed since you were a
baby. All babies are born with spaces between the bones in their
skulls. This allows the bones to move, close up, and even overlap
as the baby goes through the birth canal. As the baby grows, the
space between the bones slowly closes up and disappears, and
special joints called
sutures
(say:
soo
-churs) connect the bones.
Your Hands
As you sit and type at the keyboard, while you swing on a swing,
even when you pick up your lunch, you're using the bones in
your fingers, hand, wrist, and arm.
Each arm is attached to a shoulder blade or
scapula
(say:
sca
-pyuh-luh), a large triangular bone on the upper back corner of
each side of the rib cage. The arm is made up of three bones: the
humerus
(say:
hyoo
-muh-rus), which is above your elbow, and the
radius
(say:
ray
-dee-us) and
ulna
(say:
ul
-nuh), which are below the elbow.
Each of these bones is wider at the ends and skinnier in the
middle, to help give it strength where it meets another bone. At
the end of the radius and ulna are eight smaller bones that make up
your wrist. Although these bones are small, they can really move!
Twist your wrist around or wave and you'll see how the wrist
can move.
The center part of your hand is made up of five separate bones.
Each finger on your hand has three bones, except for your thumb,
which has two. So between your wrists, hands, and all your fingers,
you've got a grand total of 54 bones - all ready to help you
grasp things, write your name, pick up the phone, or throw a
softball!
Your Legs
Sure, your arm, wrist, hand, and finger bones are great for
picking up the phone, but how are you supposed to run to answer it?
Well, with the bones of the legs and feet! Your legs are attached
to a circular group of bones called your
pelvis
. The pelvis is a bowl-shaped structure that supports the spine. It
is made up of the two large hip bones in front and behind are the
sacrum and the coccyx. The pelvis acts as a tough ring of
protection around parts of the
digestive system
, parts of the urinary system, and parts of the reproductive
system.
Your leg bones are very large and strong to help support the
weight of your body. The bone that goes from your pelvis to your
knee is called the
femur
(say:
fee
-mur), and it's the longest bone in your body. At the knee,
there's a triangular-shaped bone called the
patella
(say: puh-
tel
-luh), or kneecap, that protects the knee joint. Below the knee are
two other leg bones: the
tibia
(say:
tih
-bee-uh) and the
fibula
(say:
fih
-byuh-luh). Just like the three bones in the arm, the three bones
in the leg are wider at the ends than in the middle to give them
strength.
The ankle is a bit different from the wrist; it is where the
lower leg bones connect to a large bone in the foot called the
talus (say:
tal
-iss). Next to the talus are six other bones. But the main part of
the foot is similar to the hand, with five bones. Each toe has
three tiny bones, except for your big toe, which has just two. This
brings the bone total in both feet and ankles to 52!
Most people don't use their toes and feet for grabbing stuff
or writing, but they do use them for two very important things:
standing and walking. Without all the bones of the foot working
together, it would be impossible to balance properly. The bones in
the feet are arranged so the foot is almost flat and a bit wide, to
help you stay upright. So the next time you're walking, be sure
to look down and thank those toes!
Your Joints
The place where two bones meet is called a
joint
. Some joints move and others don't.
Fixed
joints are fixed in place and don't move at all. Your skull has
some of these joints (called sutures, remember?), which close up
the bones of the skull in a young person's head. One of these
joints is called the
parieto-temporal
(say: par-
eye
-ih-toh
tem
-puh-rul)
suture
- it's the one that runs along the side of the skull.
Moving
joints are the ones that let you ride your bike, eat cereal, and
play a video game - the ones that allow you to twist, bend, and
move different parts of your body. Some moving joints, like the
ones in your spine, move only a little. Other joints move a lot.
One of the main types of moving joints is called a
hinge
joint. Your elbows and knees each have hinge joints, which let you
bend and then straighten your arms and legs. These joints are like
the hinges on a door. Just as most doors can only open one way, you
can only bend your arms and legs in one direction. You also have
many smaller hinge joints in your fingers and toes.
Another important type of moving joint is the
ball and socket
joint. You can find these joints at your shoulders and hips. They
are made up of the round end of one bone fitting into a small
cup-like area of another bone. Ball and socket joints allow for
lots of movement in every direction. Make sure you've got lots
of room, and try swinging your arms all over the place.
Have you ever seen someone put oil on a hinge to make it work
easier or stop squeaking? Well, your joints come with their own
special fluid called
synovial fluid
(say:
si
-no-vee-ul) that helps them move freely. Bones are held together at
the joints by
ligaments
(say:
lih
-guh-mints), which are like very strong rubber bands.
Taking Care of Bones
Your bones help you out every day so make sure you take care of
them. Here are some tips:
- Protect those skull bones (and your brain inside!) by wearing
a helmet for
bike riding
and other sports.
- When you use a skateboard, in-line skates, or a scooter, be
sure to add wrist supports and elbow and knee pads. Your bones in
these places will thank you if you have a fall!
- If you play sports like football, soccer, lacrosse, or ice
hockey, always wear all the right equipment.
-
Never
play on a trampoline. Many kids end up with broken bones from
jumping on them. Broken bones can eventually heal, but it takes a
long time and isn't much fun while you wait.
- Strengthen your skeleton by drinking milk and eating other
dairy products (like low-fat cheese or frozen yogurt). They all
contain calcium, which helps bones harden and become strong.
- Be active! Another way to strengthen your bones is through
exercise like running, jumping, dancing, and playing
sports.
Be kind to your bones, and they will treat you right!
Reviewed by:
Elana Pearl Ben-Joseph, MD
Date reviewed: August 2006
Note: All information is for educational purposes only. For specific medical advice,
diagnoses, and treatment, consult your doctor.
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